Presently, in the 3GPP (Third Generation Partnership Project), the standardization of LTE-advanced (hereinafter the LTE Release 10 specifications and the specifications of later versions will be collectively referred to as “LTE-A”), which is an evolved radio interface of the LTE (Long Term Evolution) Release 8 specifications (hereinafter referred to as “LTE” or “Rel. 8”) is in progress. LTE-A is attempting to realize higher system performance than LTE while maintaining backward compatibility with LTE.
In LTE, in downward communication from a base station to a terminal, reference signals are transmitted from a transmitting apparatus (base station) to a receiving apparatus (terminal). The primary use of reference signals is quality measurement for channel estimation for demodulation, frequency scheduling and adaptive MCS (Modulation and Coding Scheme) control.
To realize further improvement, introduction of high-order MIMO (for example, eight transmitting antennas) and coordinated multiple-point transmission/reception (CoMP) in LTE-A is under study. Consequently, in LTE-A, introduction of the CSI-RS (Channel State Information-Reference Signal) as a downlink reference signal for measuring downlink channel quality has been determined.
A user terminal receives the CSI-RS, which a base station transmits via the downlink, and, using this CSI-RS, measures channel quality such as the CQI (Channel Quality Indicator), the PMI (Precoding Matrix Indicator), the RI (Rank Indicator) and so on. The user terminal generates a CSI report, which includes measured channel quality information, and transmits the CSI report to the base station via the uplink.